Gas vs Diesel

[Baker]

I love the smell of diesel in the morning, and the rumbling of a low-revoluting engine with its watery exhaust.

Click on photo:

Me too....except to hear 2 Cummins pumped up and humming at 2400RPMs is certainly something to behold!!!!

 

[smitty477]

Me too....except to hear 2 Cummins pumped up and humming at 2400RPMs is certainly something to behold!!!!

Yes - twin turbo diesels at 2,700 sound pretty good to me as well....
but the sound of twin outboards at 6,000 rpm with the water going by at a very high rate of speed does wake you up in a large way.

 

[BandB]

As far as buying a gas boat? Nothing really I guess. There are a hand full of gas 35-45 ft boats for sale near me, but there's a reason ships, tugs and big rigs are diesel haha. I know a gas boat won't be something we take long trips on, but it would get us on the water.

As far as needing a bigger boat.... The admiral has laid down the law haha.

I would say the vast majority of us started with gas boats. I boated until I was 42 years old using only gas boats. i was on an inland lake. Every other boat there was gas.

One thing I'd be aware of in buying one is range. However, many gas boats will have more than enough range for what you plan to do. If gas was what it took to get started, that's how I'd go. We have another member who was in the process of buying a gas boat on the SC coast.

 

[Baker]

Let me put this question of more torque from diesels to bed (hah!) with a simple comparison of a gasser and a diesel of about the same hp:

A GM Vortec 5.7 used in Mercruiser, Crusader, etc gassers. It makes 292 hp at 4,800 rpm and 370 ft-lb of torque at 3,200 rpm.

A Cummins 5.9- 270 hp diesel which makes its 270 hp at 2,600 rpm and 682 ft-lb of torque at 1,800 rpm.

Similar displacement and similar hp but the Cummins makes twice the torque as the Vortec, right? Well not exactly.

The Cummins will probably be mated with a 1.5:1 transmission. The Vortec will probably be mated to a 3:1 transmission because the engine revs to almost double what the Cummins revs at rated wot hp.

So the Cummins will transmit 682*1.5= 1023 ft-lbs of torque at the prop shaft at peak. The Vortec will transmit 370*3= 1,110 at the prop shaft.

Surprise! Both engines make the same maximum torque at the prop shaft. The only difference is that the Cummins does it with the engine turning at about half the speed as the Vortec. That is why we think it is a lot more as it comes on at low speed. But the real world prop shaft effect at maximum torque is the same.

Now you can quibble.....

I am going to quibble because your numbers exist in a vacuum. In the real world, guess what??? You advance the throttles on a 40 foot gas powered boat and you can make it to full throttle and the tachs are only showing 3200...well outside of your torque curve (that looks like Pike's Peak)...and then it slowly inches up...and 5-10 seconds later you are passing 4000RPMs and finally getting up on plane. Sorry amigo. I have a friend with a newer Carver 41 but about the same weight since it is a Sedan. 375hp gas twins. And my boat will be on plane as quickly as I want it to be....on demand basically. His struggles severely. I will take the table top looking torque curve of a diesel where almost all of the horsepower resides....not just a small fraction. Because what gets things moving, regardless of gas or diesel, is horsepower under the torque curve! You will NEVER find a gasoline engine with a torque curve like this! And for planing boats, this is important!!!

 

[Ski in NC]

Baker- Many a diesel boat has torque peak occur after boat reaches planing speed. That causes them to linger on the "hump", then once over, take off like a rocket. That's not just an issue with gassers.

Late model diesels tend to be better in this regard, but still can be an issue. Worse on heavy boats with lots of power. Start planing out at 1100, torque builds at 1300, that kinda thing.

 

[ksanders]

I've slept many a night aboard our gasoline powered cruisers, and didn't die from it, and had a GREAT time.

Up to a certain size a gasoline powered cruiser makes allot of sense.

Plus!!! They are for sale at a reasoanble price, and they are fast enough to enjoy on the weekend breaks that most working folks get.

If it were not for the great time in our gasoline cruisers we would have NEVER even considered our present diesel powered floating second home.

 

[Lepke]

Besides the exploding argument, gas engines often suffer more in moist environments, especially tropical. Electronic ignition helped but doesn't totally solve the problem. When I was young, I ran a 50' boat with twin Chrysler Crowns, 6 cylinder flathead. Later changed to DD 453s and fuel was 1/2 and plus 2 kts in speed.
Traveling a long distance, like the loop, in a 40', you will burn much more fuel than diesel at the same speed. Enough to maybe make up the difference in cost. Could be 6 gallons an hour per engine, more than I burn in an 83'.
You absolutely have to use a fuel conditioner to keep the gasoline burnable if stored for any time. Thanks to the EPA. Your tax dollars at work.
On the other hand, if buying gas is the difference in being able to buy a boat, I'd go with gas.

 

[Art]

IMO


For boats 40' and below... gas engines are OK [of course... so are diesel].


Gas engines in above 40' need to be big cubic displacement, like 460 Fords, 454 GMs, 440 Chryslers, 430 Buicks and the like. These big gas engines in general drink much fuel in order to get speed... like pouring gas through a small funnel.


On the other hand: For boats 40' and below there are smaller gas engines that can be fairly economical, like 350 GMs, 351 Fords, 360 and 318 Chryslers. These engines when kept to [at or over] 1.4 per CID to 1 HP ratio can last a long time. With any gas engine the closer to 1 per CID to 1 HP ratio things get the more fuel use and the more stress that can be placed on engine internals which lowers their life spans. When gas engines get into the .5 CID to 1 hp ratio [that's 700 HP in a 350 CID GM] is when longevity no longer exists and fuel use goes over the top.

 

[Baker]

I've slept many a night aboard our gasoline powered cruisers, and didn't die from it, and had a GREAT time.

Up to a certain size a gasoline powered cruiser makes allot of sense.

Plus!!! They are for sale at a reasoanble price, and they are fast enough to enjoy on the weekend breaks that most working folks get.

If it were not for the great time in our gasoline cruisers we would have NEVER even considered our present diesel powered floating second home.

So you're saying it is a "gateway" boat!!!.. :lol:

 

[gaston]

Id rather a gas boat than no boat .

 

[FF]

"Up to a certain size a gasoline powered cruiser makes allot of sense"

Its more the speed required than the size.

A boat that will climb up and plane requires far more HP than can be found on a long term basis from gas.

Over about 250 hp on a cont basis diesel makes sense , it is all that is aviliable.

Or over 1000 hours a year diesels will be rebuilt less often than gassers.

For a displacement cruiser a 60 ft gasser would be easy to contemplate .

At say 30-45 tons displacement about 120-150 cont HP would be required , no sweat long term for a modern 300CI gasser.

For the 200 hours a year cruiser it would be more than 20 years of low cost maint , low cost parts , lube oil , anti freeze and even smaller batteries.

 

[Nomad Willy]

As far as buying a gas boat? Nothing really I guess. There are a hand full of gas 35-45 ft boats for sale near me, but there's a reason ships, tugs and big rigs are diesel haha. I know a gas boat won't be something we take long trips on, but it would get us on the water.

As far as needing a bigger boat.... The admiral has laid down the law haha.

There's a reason ships use very different anchors as in stockless types (like a Navy anchor) but they are only rarely seen on pleasure boats.
There's a reason pleasure boats use electric winches and ships use hydraulic.
There's a reason you don't see diesel engines in ski boats.
And there are reasons most planing craft use gasoline engines. Good reasons.

But whatever you use it should fit your needs.
If you don't like lots of noise, fuel smell, vibration, high cost and excessive weight, get a gas engine. No need to do what others do (unless that drives you) or what others want if you understand what you want. However, one shouldn't convert a big trawler to gas and then wonder why it doesn't sell later on.

 

[Art]

There's a reason ships use very different anchors as in stockless types (like a Navy anchor) but they are only rarely seen on pleasure boats.
There's a reason pleasure boats use electric winches and ships use hydraulic.
There's a reason you don't see diesel engines in ski boats.
And there are reasons most planing craft use gasoline engines. Good reasons.

But whatever you use it should fit your needs.
If you don't like lots of noise, fuel smell, vibration, high cost and excessive weight, get a gas engine. No need to do what others do (unless that drives you) or what others want if you understand what you want. However, one shouldn't convert a big trawler to gas and then wonder why it doesn't sell later on.

That is a "Catch 22"

 

[Sealife]

I can't think of a "trawler" that has gas engines. Not meaning any offense....If we are talking planing cabin cruisers, sure.

 

[eyschulman]

I would think a trawler over 35 ft with gas engine would be difficult to sell at a good price on the used market No matter what the logic behind the motor is. A planning craft or more conventional cruiser type used like a trawler no problem if gas. Don't ask me to define trawler. I am not going to wait for a reply I am going out sailing and not on a trawler.

 

[BandB]

I can't think of a "trawler" that has gas engines. Not meaning any offense....If we are talking planing cabin cruisers, sure.

A lot of non-planing and semi-displacement boats with gas. Nearly all houseboats have gas. Plus boats like Sea Ray and some Mainship. A lot of boats that are excellent options for coastal cruising.

 

[ksanders]

So you're saying it is a "gateway" boat!!!.. :lol:

Yes!

We all know how this works. We start with a desire to go boating and or in my case fishing.

We buy a boat and have allot of fun. Then we think "what if we could spend the night on the boat" so we buy a bigger boat with sleeping and a head and a minimum galley.

We like that so much that we think we'll have more fun in a bigger boat.

Fast foreward a decade and we're flat boating addicted, our lives are "ruined". We have a boat that takes all our money and all our time.

So we quit work "retire" to give us more time for our addiction.

 

[Ski in NC]

Wisdom is achieved when one's new boat is smaller than their last...

 

[Art]

A lot of non-planing and semi-displacement boats with gas. Nearly all houseboats have gas. Plus boats like Sea Ray and some Mainship. A lot of boats that are excellent options for coastal cruising.

Yup! No muss no fuss gas engines suffice well in our 34', 21K loaded lbs., planning hull, self contained, tri cabin Tollycraft pleasure cruiser. Two 100 gallon fuel tanks. 77 gallons water. 30 gal holding tank. Draft 2' 10".

Twin 350cid, 255 hp. nearly 3 nmpg running one engine at 4.5 to 5 knots. Over 2 nmpg on both engines at 6.5 to 7 knots [7.58 is calculated hull speed]. 1 nmpg at 16 to 17 knots planning cruise. WOT = 22 to 23 knots at OMG gph!

 

[Nomad Willy]

THREE nautical mpg?

Art I only get one w my Willard.
But I don't ever cruise at 5 knots.

 

[eyschulman]

Now that I am nice and mellow and back from sailing on Lake Washington back to the gas vs. diesel thing. The complication as I see it is that this site has a lot of boats or at least boaters that believe they are trawler owners. I for one do not know what a recreational trawler is with any great accuracy. I see boat classification by ability and use patterns. A power boat designed to cross open oceans and operate independently long distance in potential rough weather is one category which if recreational trawler had a meaning might fit here. The next category is not as clear cut and includes boats capable of live aboard for reasonable periods while cruising coastal and inter-coastal. This group I further subdivide into fast-medium and slow speed. Some of these boats I might consider qualifying as Rec. trawlers what ever that is, others not. Another measure I apply to a boat or boat design is How much of the boat is based on a cottage . The is no fixed point where I start thinking house boat but there are certainly enough boats in that last category. So is there such a thing as a houseboat trawler? Why does all of this come to mind in a discussion about gas vs. diesel? Because the choice between the two will often hang on what actual type and category the boat fits into as has been pointed out by many of the above posts. True fishing trawlers are probably almost all diesel powered for obvious reasons. Open ocean long distance rec. boats all diesel and after that a lot of muddy water.

 

[FlyWright]

Salty, what you need to take away from this is that it can be done...quite easily. But there are compromises. The biggest, IMHO, is safety. Diesels generally do not explode. In my relatively short boating career, I have seen, with my own eyes, 3 gas boats blown sky high with severe injuries and fatalities. Another part of the safety equation is Carbon monoxide. Diesels barely produce any but gassers produce a lot. Would you feel comfortable laying on the hook with a gas engine(generator) running in your bilge...with your entire family on board??? I would not. SO peace of mind can be worth a LOT.

One last thing is a larger gas powered boat, if run up on plane, will struggle to get up on plane. I just feel better knowing that diesels can handle that work...easily...versus gas engines that are just barely getting the job done. PSNeeld's work boat is likely all fiberglass and engine...that is it. IOW, it is light. You put a 40 foot aft cabin motoryacht on top of a couple of gas engines and that is the reason they are worn out at 1500 hours...if you're lucky.

All true, but if it means getting on the water sooner than later, I vote gasser. It allows the lifestyle and learning the chance to begin. The real risks (BANG! and CO) need to be seriously paid attention to and mitigated. Sitting on the dock waiting for a diesel boat teaches nothing but patience.

So you're saying it is a "gateway" boat!!!.. :lol:

Id rather a gas boat than no boat .

If I never bought a gas powered Sea Ray runabout, I'd never have a twin diesel trawler. Sometimes you need to learn how to crawl before you can walk...then get good at walking before you run.

If life interferes along the way in the process, at least you had some time doing what you love. If not, you just got a head start on the rest of your life. It's a win-win....as long as you don't kill yourself in the gasser!

 

[Miz Trom]

Don't know if you've seen the TT35. This is with the standard twin Suzuki 60hp outboards. Having boated primarily in Florida, the low draft of 16" appeals. The fuel efficiency is pretty interesting, too.

TT35 Key Features - Great Harbour Trawlers

TT35 Test Report - Great Harbour Trawlers

TT 35 Performance - Great Harbour Trawlers

 

[Ski in NC]

Those numbers look great for a 37. But that is for a very light ship. Add a full cruising load and the numbers will drop fast.

 

[Nomad Willy]

A 36' cruiser going 50mph w a pair of OB's. Hmmmm

 

[FF]

"However, one shouldn't convert a big trawler to gas and then wonder why it doesn't sell later on."

A knowledgable owner should not be that hard to find.

 

[Nomad Willy]

FF it would largely depend on price don't ya think?

 

[Donsan]

A 36' cruiser going 50mph w a pair of OB's. Hmmmm

Ehemm....where was the 50mph comment made?

 

[Art]

Ehemm....where was the 50mph comment made?

Chart on post # 53. 3/2 of the way down, center column... listed "Top Speed". I believe Eric was rounding up the 49 mph quote.

 

[Donsan]

Chart on post # 53. 3/2 of the way down, center column... listed "Top Speed". I believe Eric was rounding up the 49 mph quote.

Okay, fair enough. Wish they put the brand name on the columns. It would be nice to read more about that boat.